PTL 1 proposes a solid-state image pickup element in which pixels (hereinafter also referred to as distance measurement pixels) having a distance measuring function are arranged in part or all of pixels in the image pickup element to detect the distance to a subject by a phase difference method in a digital still camera or a digital video camera. The distance measurement pixels each include multiple photoelectric converters and are each configured so that light fluxes that have passed through different areas on a pupil of a camera lens are led to different photoelectric converters.
Optical images generated by the light fluxes that have passed through the different pupil areas are acquired from signals acquired in the photoelectric converters included in each distance measurement pixel. Such optical images are hereinafter also referred to as an “A image” and a “B image” and collectively also referred to as “AB images.” The amount of displacement between the AB images (hereinafter also referred to as an “amount of image displacement”) is detected.
The amount of image displacement is converted into an amount of defocus via a conversion factor to calculate the distance to the subject. With this method, since it is not necessary to move the lens in order to measure the distance, unlike methods using contrast in related art, the distance measurement is enabled at high speed and with high accuracy.
The accuracy of distance in the measurement is improved by acquiring the accurate amount of image displacement and an accurate base line length.
PTL 2 proposes a method of calculating the base line, which is the conversion factor, on the basis of information about the distribution of the light fluxes in an imaging optical system that forms an image of a subject on a solid-state image pickup element and lens aperture information to improve the accuracy of distance.